According to International Telecommunications Union (ITU) Telecommunications standard (ITU-T) G.998.2 (2005) bonding of a plurality of physical lines is located in between the physical layer (layer 1) and the data link layer (layer 2) at the γ interface.
Bonding above the physical layer or at an upper edge of the physical layer has certain restrictions and drawbacks. E.g., it can be required to provide differential delay compensation buffers to cope with the required differential delay of up to 10 milliseconds for high bit rates. In particular, big differential delay compensation buffers may be required in a scenario where 10 ms impulse noise impacts one of the bonded physical lines, but not other bonded physical lines.
A further drawback is that adding another physical line to a bonding group can be comparably slow. Thus, switching between bonded mode and unbonded mode may not be possible or only possible to a limited degree during Showtime.
Further limitations and drawbacks relate to operation of the various physical lines in different modes. E.g., within existing reference implementations of bonding, operation may be limited to either full power transmission for all bonded physical lines or low power mode for all bonded physical lines. A combination of full power mode for one more bonded physical lines on the one hand side, with low power mode for further bonded physical lines on the other hand side may not be possible or only possible to a limited degree.
A further drawback of existing reference implementations of bonding relates to additional bonding overhead introduced. The bonding overhead reduces the throughput of applications implemented on the physical lines of a bonded group. E.g., fragmentation using sequence numbers identifying fragments may be used for distributing data between bonded physical lines; sequence numbers may require additional overhead.